U.S. President Barack Obama had stern words for his Russian counterpart Vladimir Putin over Russia’s actions in Ukraine, following a meeting Thursday of G7 leaders in Brussels, Belgium, from which Russia was excluded. Putin “has a chance to get back into a lane of international law,” Obama said. But for this to happen, he said, Putin must take steps over the coming weeks that include recognizing Ukraine’s new President-elect Petro Poroshenko, stopping the flow of weapons over the border into Ukraine, and ceasing Russian support for pro-Russia separatists in Ukraine. “We cannot simply allow drift,” Obama said, speaking alongside British Prime Minister David Cameron following bilateral talks. “The mere fact that some of the Russian soldiers have moved back from the border and that Russia is now destabilizing Ukraine through surrogates, rather than overtly and explicitly, does not mean that we can afford three months, or four months, or six months, of continued violence and conflict in eastern Ukraine.”

If Russia does not de-escalate the situation, the G7 leaders are united and ready to impose further painful economic sanctions, Obama said, with consequences for the Russian people. “Today, in contrast to a growing global economy, a sluggish Russian economy is even weaker because of the choices made by Russia’s leadership,” he said. Putin was excluded from what was originally planned as a G8 summit in Sochi, Russia, as part of measures to sanction Moscow over its annexation of Ukraine’s Crimea region. It’s the first time in some 20 years that Russia has not been part of the meeting of world economic powers, Obama said, adding that the step is warranted because Moscow’s actions have violated international law and gone against the group’s principles.

President Barack Obama meets with British Prime Minister David Cameron at the G7 summit

European Commission President Jose Manuel Barroso, left, and European Council President Herman Van Rompuy, right, welcome President Barack Obama at the G7 meeting at the European Council building in Brussels